In automation technology, especially in process automation, field devices are often applied, which serve for determining, optimizing and/or influencing process variables. Serving for registering process variables are sensors, such as, for example, gas sensors, gas analyzers, fill level measuring devices, flow measuring devices, pressure- and temperature measuring devices, pH-redox potential measuring devices, conductivity measuring devices, etc., which register the corresponding process variables, fill level, flow, pressure, temperature, gas quantities and gas qualities, pH-value, and conductivity. Serving for influencing process variables are actuators, such as, for example, valves or pumps, via which the flow of a liquid in a section of pipeline or the fill level in a container can be changed. Referred to as field devices are, in principle, all devices, which are applied near to the process and deliver or process information relevant to the process. In connection with the invention, field devices thus include also remote I/Os, radio adapters, or, generally, devices, which are arranged at the field level. A large number of such field devices are produced and sold by the firm, Endress+Hauser.
Known from European patent EP 1 629 331 A1 is a variable field device for process automation technology. The individual functions of this field device are distributed. The actual field device provides only a few basic functions, e.g. the measured value production, while application-specific functionalities, such as e.g. frequency- or pulse outputs, are embodied as separate functional units, which are arranged spatially separated from the field device. Field devices and functional units are connected to a corresponding communications medium for the purpose of data exchange. The communications medium is a two-conductor supply line. Alternatively, a number of data channels are provided on the communications medium, so that multiple access to the connected units is possible. In this way, the field device is variably and application-specifically configurable.
Known from German patent DE 10 2006 016 381 A1 is a measuring apparatus for determining and/or monitoring at least one process variable, wherein the measuring apparatus includes as integral components a sensor unit, an in/output unit and a display unit. The sensor unit produces raw, measured values, wherein from the raw, measured values the information concerning the process variable is producible. Data are received or forwarded via the in/output unit. Presented on the display unit is the information representing the process variable, as provided by a control unit. Communication between the sensor unit, the in/output unit and the display unit, on the one hand, and the control unit, on the other hand, occurs via one of the fieldbusses customary in automation technology.
In the field of gas analysis, reliable optical methods are applied, in the case of which light is led from a radiation source through a measuring chamber through which a gas mixture is flowing. Along this radiation path, certain specific gas component dependent absorptions of the light are effected and registered with a detector. From the amount of absorption of certain wavelengths of the light, the specific weight of individual components of the measured gas and their concentrations can be deduced. There are some known methods for measuring the gas concentrations, such as e.g. Non-Dispersive UltraViolet spectroscopy—NDUV, Non-Dispersive InfraRed spectroscopy—NDIR, as well as also laser absorption spectroscopy—TDLAS—Tunable Diode Laser Absorption Spectroscopy. Moreover, there are other methods, which will not be explored further here.